Method of spinning viscose



Jan. 8, 1952 I cox 2,581,835

METHOD OF SPINNING VISCOSE Filed March 22, 1946 INVENTOR. Nornzam, Lg uls 60a:

ATTOR Er Patented Jan. 8, 1952 METHOD OF SPINNING VISCOSE,

Norman Louis Cox, Claymont, DeL, assignor to E. I. du Pont de Nemours & Company, Wil-, mington, DeL, a corporation of Delaware Application March 22, 1946,-Serial No. 656,478

11 Claims. (01. 18-54) This invention relates particularly to improve ments in the spinning of filaments from unripened viscose.

It is customary in theart of spinning regenerated cellulose filaments and yarns to utilize viscose which has been ripened, i. e. aged fora certain period of time, in order to produce optimum properties in filaments andyarns, particularly when using. coagulating baths which comprise sulfuric acid and sodium sulfate, which baths, according to modern practice, also preferably contain one or more salts of divalent metals, e. g. sulfates of zinc, ferrous iron, nickel, manganese, chromium and magnesium; zinc sulfate particularly is widely used in sulfuric acidsodium sulfate spinning baths. Unless the viscose is ripened sufficiently, the filaments and yarns produced are of poor quality and unsuitable for use in the textile industry. For ex-.

ample, when an unripened (i. e. green) viscose prepared from sodium cellulose xanthate (commonly termed cellulose xanthate herein) which is produced by combining alkali cellulose with 35% carbon disulfide based on the weight of bone dry cellulose in the alkali cellulose and which has a salt index of 8.0 to 10.0, a xanthate sulfur concentration of 1.4% and a sodium trithiocarbonate content of 0.75%, is spun into baths containing an appreciable ferrous and/or zinc sulfate content,'thin skinned yarns with inferior properties are obtained. However, when the salt index andxanthate sulfur concentration are reduced throughripening to 5.0% and 1.1%, respectively (the ripening step being accompanied by an increase in sodium trithiocarbonate content of from about 0.75% to about 1.3%), yarns having thick'skins and excellent physical properties are obtained. The importance of skin thickness will be appreciated from the. fact that, in general, when theskin represents 'arelatively large proportion of .the cross-section of the filament, the filament and yarn properties are acceptable. 'In good yarn, particularly in high tenacity yarn for tire cord, the skin constitutes ripened further, the level'of properties fall off,

sharply.

It is desirable to use viscose having as high a' salt index (and as high a xanthate sulfur .concen-i' tration since this is directly proportional to the salt index) a is consistent with optimum yarn properties when using the spinning baths known to-the art, particularly since the diminution in. the ripening time or the elimination of ripen-;-,;

ing would effect a substantial economy. However, in viscose as'it is normally prepared, the

ripening step,h as been considered necessary. in

order to reduce'the xanthate sulfateconcentration (saltindex) to an optimum value for spin?" ning. 'The accompanying increase in sodium trithiocarbonate, which is generated during the xanthatin'g and ripening. step, has been consid;

ered a necessary evil since the sodium trithio carbonate may cause excessive gassing and the development of 'defects'in the filaments I and yarns. It has now been discovered, contrary to the generally held views, that if additional sodium trithiocarbonate is incorporated into ripened viscose, saidunripened viscose can "be" spun with-little or'no ripening (e. g. at'a high salt index and xanthate {sulfur concentration) to producethick skinned filaments of excellent quality, particularly if a spinning bath containing zinc sulfate is used. The use of added sodium trithiocarbonate is of advantage also even where the viscose issubjected to a substantial degree of ripening.

object of this invention is to improve the production of various'articles from viscose. Another object of this invention is to utilize viscose having a high salt index for the production of; shaped articles, particularly filaments and yarns acceptable for use in the textile industry. still another'object is concerned with the utilization of substantially unripened viscose for thepro}; ducti'on of filaments andyarns and'other products. Further objects of the invention are im-" still further object is to eliminate the time-con suming step of ripening the viscose in the manu= facture of various products and particularly of regenerated cellulose filaments. Other objects of the invention will appear hereinafter.

The objects of the invention are accomplished in general by making up a viscose containing dissolved therein an added amount of an alkali metal trithiocarbonate, extruding. the viscose, preferably without substantial ripening, into a sulfuric acidsodium sulfate bath preferably contain ng zinc sulfate or other sulfate of a divalent metal, stretching the filaments if desired, preferably in a two-bath systemin which all 'orfa hours.

major part of the stretching occurs in the second bath, and collecting the yarn in any suitable fashion.

In the drawings:

Figure 1 illustrates diagrammatically a magnified cross-section of a filament produced in accordance with the present invention which has been dyed and reswollen in water, the central shaded portion representing the core and the unshaded outer portion representing the skin, and

Figure 2 shows, by comparisorr- -a similarly magnified cross-section of a dyed and waterreswollen filament produced fromflunripenedrviscose which has not been modifiedin accordance with the present invention and in which the shaded portion illustrates the core and" the ran-- shaded portion the skin of the filament.

The following examples illustrate various:

methods of applyingthe principles of the invention. In theexamplesand elsewhere-through" out the specification, parts, proportions and per'--.

centages" are by -weight unless otherwise speci fiedi if i "EXAMPLE; I

cotton linters viscose cohtaining 7% cellulose, 6% total causticisodiumf hydroxide), this viscose being commonly called. 7 6' viscose, and

added sodium trithiocarbonate is prepared in the following manner. Alkali cellulose aged to give the idesired viscosity (40 .to' 60 poises) is xarithated for two and onehalf hours, using 35% carbon disulfide, based onthe bone dry cellulose in the alkali cellulose. The xanthate crumbs are-dissolved in an aqueous solution of caustic .sequently, the ratio of carbonate to trithiocarbonategjn the yiscose. described herein has not ee d turbe Aft r, mixi t r. one to .0118

and a half hours f at 0 C,, the ireghly prepared viscose is. filtered while it is cold, deaerated. and then, to; preyent ripening, kept at 0 C. until spun, The viscose is spun into filaments by extruding through a 100-hol d ;spinneret having holes of 0.0025inch. diameteninto primary coagulating and regenerating baths havinga temperature of 50 C.. and respectively comprising (1) 6% sulfuric acid, 14%, sodium sulfate and 15% zinc suliate. and (2) 9 .suliuric acid, 22% sodium sulfate, 1% zinc sulfate and 5% ferrous sulfate. Thebundle of filaments is given a bath travel of 28 inchesby using a roller guide and is passed from the bathto afeed wheel rotating at a peripheral speedof 485"inches per minute. The filaments are then carried through a hot water bath and. wound upon a bobbin at such a speed as to give" 80%fs'tretch beyond the feed Wheel. The resulting'regei'ierated gel yarn is washed free of acid and salt, processed for further purification and is. then collected and dried on a bobb'infThe dried yarn is twisted. four turns. per inch and tested after conditioning. at

21 C. andv 60%.rielatil7ehi1tl1idity for forty-eight The properties ofthefyjarn prepared from the 4 viscose, modified as described in this example, and yarn similarly prepared respectively from green, unmodified viscose and ripened, unmodified (control) viscose are listed in the first, second and third columns respectively in the accompanying Table I. It Will be seen in the table of properties that the level of properties is lowest for the yarns from unripened, unmodified viscose and is highest for the yarns from unripened, sodium trithiocarbonate modified viscose. The properties for the yarns from ripened, control viscose (index 5.0) are intermediate. In addition to improved yarn properties, other advantages to the use of the modified, green viscose are the elimination of the ripening step and improvement (i. e. reduction) in wet contraction as compared with yarn made from ripened viscose; wet contraction signifies shrinkage or loss in length resulting from the wetting of dry yarns and filaments and drying the wetted yarns and filaments without tension, this shrinkage being accompanied by increase in elongation and loss in tenacity. Low wet contraction is particularly Table I COAGULATING BATH 6-14-15 (H2SO .NazS O4'ZnSO4) Unripened Unripenecl Control Visose: 7

Salt Index; I 7. 7 8. 4 5.0 Per Cent Xanthate Sulg fun".. 1.35 1. 40 1.10- Per Cent NazCS; Added 1.44- 0 '0 Per Cent NazCSs Totalj. 2. 28 O; I- Yarn: v V

Tenac ty, g. p. (1;, dry 3:93 3'. 20 3. 71 Tenacity, g. p. d., wet 2.6L 7 2.14 2. 52- Elongation Per Cent, dry. 9; l 10.4 9.1 Elongation Per Cent, wet. i 21 4 24. O 23. 2 Per Cent Slcln 1 00 0 0 0A G ULATIN G BATH 9-22-1-5 (H28 O -NazS GrZnS OrFeS O4) Viscose:

Salt Index. 7.7 8. 4 5.0 Per Cent XanthateSulfur 1.35 1.40- 1 .10 Per'Cent NazCSaAddedi. 1.454 0 0 Per Cent NazOSs Total... 2. 28: z 0.85. 1 30 Yarn: V

Tenacity, g; p; d., dryi... 3194 313p 3. 73 Tenacity; g. p. d., Wet.. I 2451-- 1.86- 2. 29- Elongation Per Cent, dry. 8. 0 7. 3 7. 7 Elongation Per Cent, wet. l8. 1 l4. 2 1'8: 1' 7 Per Cent Skin 50-60 3040 40-50 EXAMPLE II 7-6 viscose" modified with alkali trithiocarbon-= ate is prepared and spun into a 6.0-14-15 (sulfuric acid-sodium sulfate-zinc sulfate) coagulating bath under conditions otherwise as in Example-I and the-yarns'are processed in the man'- ner described in Example I except that the 1.44% of sodium trithiocarbonate" which is added at the time of mixing is froma different source; It is prepared commercially by reacting one mol of sodium sulfide and one mol of carbon disulfide and contains only a small. amount or sodium carbonate. It will be noted in Table II below, which compares the modified yarns with yarns similarly prepared from green, unmodified. viscose and from ripened, unmodified-, control viscose, that the commercial sodium tri-thiocarbonate produces the same improvements as those described in'E'xample' I.

Table II Modified Unmodified Ripened Unripened Unripened Control Viscose;

Salt Index 9. 6 8. 4 5.0 Per Cent Xanthate Sulfur 1. 4 1. 4 1.1 Per Cent Na CS; Added l. 44 0 Per Cent N azCSa Total... 2. 31 0.85 1. 30 Yarn:

Tenacity, g. p. d., dry 3. 82 3.20 3. 71 Tenacity, g. p. d., wet Y 2. 60 2.14 2. 52 Elongation Per Cent, dry- 11. 4 10. 4 9. 1 Elongation Per Cent, wet. 25. 0 24. 0 23. 2 Per Cent Skin... 100 30-50 80-90 EXAMPLE In The cotton linters viscose described in Example II, 1. e. containing 1.44% of added sodium trithiocarbonate, is spun into filaments, using all conditions for producing and processing it as in Example II except that the acidity in the high zinc bath is increased from 6.0 to 9.5% sulfuric acid. The properties of the yarns, as well as those from the ripened, control viscose and the unripened, unmodified viscose are tabulated below. One advantage of the use of unripened, modified viscose is the fact that yarns with thicker skin and superior properties are obtained at the higher bath acidities under which conditions it is possible to employ high, commercially feasible spinning speeds in the high zinc bath.

Xanthation is carried out in the presence of 50% carbon disulfide, based on the bone dry cellulose, and the xanthate crumbs are dissolved in a caustic solution of sodium trithiocarbonate to give a '7-6 viscose. In an unripened state, this viscose contains 1.82% xanthate sulfur and 2.90% sodium trithiocarbonate. Using all conditions for producing and processing as in Example I, this unripened, sodium trithiocrabonate modified viscose is spun respectively into the high zinc and ferrous sulfate baths. Two viscoses (ripened and unripened) made from cellulose xanthate produced by combining alkali cellulose with 50% carbon 'disulfide and dissolved in caustic free from added sodium trithiocarbonate are prepared and spun for comparison, the results being given in the following Table IV. It will be seen that the level of properties for the yarns from the unripened, modified viscose is higher than those for the unripened and the ripened, but unmodified control yarns. In the iron bath, the addition of sodium trithiocarbonates to the green viscose increases the skin thickness more than 100% and makes it possible to eliminate the long aging cycle which is necessary for high-carbon, disulfide viscoses.

Table IV ooxocnxrmo BATH 644-15 H,so.-'Na,so.-znso.)

COAGULATING BATH 9-22-1-5 (H:SO Na;SO ZnSO4FeSO4) Viscose:

- Salt Index 18.0

Per Cent Xanthate Sulfur 1.82 Per Cent N23205: Added. 1.44 Per Cent NflzGSa Total... 2. 9 Yarn:

Tenacity, g. p. d., dry. 3. Tenacity, g. p. d., wet.-.. 2.31 Elongation Per Cent, dry. 9. 4 Elongation Per Cent, wet. 20. 3

EXAlVIPLE V Cotton linters viscose containing 7% cellulose. 6% total caustic and 0.32% of added sodium trithiocarbonate (the later being included in the total caustic content) is prepared following the method described in Example I. The viscose is ripened as is normally done for unmodified viscose and spun into filaments. All conditions for spinning and processing as in Example I are used. It can be seen in the following Table V, which lists the properties of the modified yarns asv well as those of similarly prepared yarns made from unmodified green and control viscoses, that measurable improvement can also be obtained in physical properties by adding sodium trithiocarbonate to viscose which has been given normal aging.

Table V COAGULATING BATH 6-14-15 (HzSO4NazSO4ZnSO4) Modified Ripened Unmodified Ripened Viscose:

Salt Index Per Cent-NazCSa Total. Yarn:

Tenacity, g. p. d., dry.

Tenacity, g. p. d., wet.

Elongation Per Cent, d

Elongation Per Cent, we

Per Cent Skin COAGULATING BATH 9-22-1-5 (H28O4-NagSO4-ZnSO4FeSO4) Viscose:

Salt Index Per Cent Xanthate Sulfur. Per Cent NazCS; Added..

Per Cent Na OSa Total Yarn:

Tenacity, g. p. d., dry...

Elongation Per Cent, dry Elongation Per Cent, we Per Cent Skin HUI EXAMPLE VI zinc sulfate to form. filaments. The spinning and processing conditions are the same as those described in Example I. The addition of sodium trithiocarbonate gives large improvement in skin thickness and physical properties in yarns which are spun at high bath acidity as is seen in the following Table VI which compares such yarn with yarn made from similarly ripened but modified viscose. One advantage of this procedure lies inthe fact that the higher bath acidity permits higher spinning speeds.

, Table VI Modified Unmodified V Ripened llipened Viscose:

Salt Index 5. O 5.0 Per Cent Xanthate Sulfur .l I 1.1 1.1 Per Cent NazCS Added lQl 0.0 Per Cent NazOsa Total 2. 4 1.3 Yarn:

Tenacity, g. p. 11., dry l. 3. 94 3, 50 Tenacity, g. p. (1., wet 2. 74 2. 08 Elongation Per Cent, dry 8. 5 8.6 Elongation Per Cent, \v- 19.7 17.3 Per Cent Skin l 60-70 40-50 The term caustic ,as'used throughout the specification means sodium hydroxide.

The term unmodified as applied to viscose throughout the examples means viscose which has not been'modifiedby the addition of sodium trithiocarbonate Whereas the modified viscose contains the added sodium trithiocarbonate.

The expression 6-14-15, for example, ap-

plied to the coagulating bath signifies, 6% sulfuric acid, 14% sodium sulfate and 15% zinc sulfate in theaqueous bath and' 'the expression 9-22-1-5,- for example, applied to the coagulating bath signifies 9% sulfuric acid, 22% sodiumsulfate, 1% zinc sulfate and 5% ferrous sulfate; other similarexpressionshave a corresponding significance; the sulfuric acid content is calculated-asH2SO4.

In all the examples and elsewhere in the description, the sodium hydroxide (or caustic) content of the viscose, e. ,g. 6% as described in the examples, includes the free sodium hydroxide and the sodium (calculated as sodium hydroxide) combined in the form of sodium carbonate, sodium trithiocarbonate (including the added amount) and sodium cellulose xanthate; and the per cent by weight of sodium trithiocarbonate and of xanthate sulfur are percentages based on the weight of the viscose.

The examples specifically illustrate the addition of sodium trithiocarbonate as a modifier to the viscose. The invention contemplates a like addition, in place of sodium trithiocarbonate, of the trithiocarbonate of other alkali metals as well as other water soluble trithiocarbonates, e. g. potassium trithiocarbonate and lithium trithiocarbonate.

. Either the product obtained by the reaction of carbon disulfide and sodium hydroxide, which contains one mol of sodium carbonate for every two mols of sodium trithiocarbonate, or the commercial product of Example II containing much less sodium carbonate, is effective in the practice of the invention.

The amount of alkali trithiocarbonate which should be added to the viscose to secure the best results in accordance with this invention de pends to-a large extenton the amount of carbon disulfide used in, the preparation of the viscose, the latter amount.formostcommercial iscosesbeinginthe -ranse30f'25.% to 50% of carbon disulfide, based n the weight of the cel--- lulose. In explanation, the less carbon disulfide used for preparing the cellulose xanthate the lower is the resultant xanthate sulfur content, and the amount'of alkali trithiocarbonate needed decreases as the xanthate content diminishes. Thus, for a 25% "carbon disuliide unripened viscose, the total sodium trithiocarbonate present, including that which is added, should be not less than 1%, based on the weight of the viscose, in order to efiect substantial improvements in spinning; for a carbon disulfide viscose, the total sodium trithiocarbonate present should be at least 1.1%, and for a carbon disulfide viscose, at lea st 1 .3%. Generally speaking, the amount'of sodium trithiocarbonate hich a dd 1 green. v cose qmpe e as to yield la .vi'scosehaving.slit" "content'pf odiu trith oc b i xi s 1 3%"iei d' preferably within the rang dof 1.5% (to 3%. Vi hile'there is no critical'f upper limit, itis pre; f erred that the total trithioc'arbonate in thev'is cose shall not exceed 3% of th'e weight of the viscose..

As is pointedoutabove, unripened viscose cone talu ajcs i i nt of o m t iihi ta dnate, eQg. about 0.85% for; most commercial,vis-' containing the same weight content of combined trithiocarbonate radical may be used. Generally speakin h amount'of d d alka 31 9 bonate used is as low as possible to accomplish the purposes of the invention.

It has been observed that the optimum concentration of sodium trithiocarbonate needed to give normal filament formation and excellent properties rises as the xanthate sulfur content, i. e. the salt index, is increased. The salt index of the viscose to be spun is preferably 6.0'or above and may go as high as 20.0. Salt index is determined by the standard sodium chloride method of Reinthaler-Rowe, Artificial Silk, 1928, page 69, which is described as follows:

The salt index i hat oncent at o in er c n of sodium chloride at which coagulation in the form of flocks .(white star like particles) first occurs. It is determined ,by-shaking mixtures of 1.0% so i m vchloride an Wa er vi e drop of viscoseior thirty seconds, and with each succeeding test, increasing the proportion of salt solution until one or two flocks are visible. As the xanthate substitution of the cellulose is increased, it requires higher salt concentrations to bring about coagulation. v

Viscose used in the preparation of filaments by this invention may be a variety of types; for example, it may be made from wood pulp, cotton lint-ers, mixtures of the two or even other types of cellulose. The composition of the viscose may also be varied widely. Forexample, it'may have a cellulose content of from .4% to 9% (combined as sodium cellulose xanthate) andan alkali content of, from 4% to 8%. The amount of carbon disulfide used in xanthation can be from 25% to %,based on the bone dry weight of the cellulose inthe alkali cellulose, this basis also being that used in the examples in referring to per cent carbon disulfide. It has been found that the higher thexanthate sul u co ten or.

salt index of a viscose the greater are the improvements that can be obtained by adding sodium trithiocarbonate. One will normally use 30% or greater amounts of carbon disulfide,

based on the dry weight of the cellulose, in

xanthation, to obtain salt indices of 5.0 or over in unripened viscose. It has been shown in the examples that added sodium trithiocarbonate is effective in viscose showing salt indices from 5.0 to 20.0, but the advantage of the invention is present with spinnable viscoses of lower salt index. It is preferred that viscoses prepared in accordance with the invention be spun at a salt index of 6.0 or higher.

If desired, unripened viscose may be purified prior to the addition of sodium trithiocarbonate by washing the xanthate crumbs with methanol, then with ether, drying and dissolving in alkali. Modification of this purified viscose with sodium trithiocarbonate gives the same results of increase in yarn skin thickness and improvement in yarn properties.

Where relatively large amounts of sodium trithiocarbonate are present in the viscose, e. g. 2% or more, it is preferred that more than 4% sodium hydroxide be present in the viscose to prevent excessive gas formation due to the evolution of hydrogen sulfide. Sodium sulfite may also be used in the viscose to reduce gassing.

While the invention is most particularly applicable to continuous filaments and yarns, it may be applied to the production of staple fibers and is of benefit in the production of films, sponges and other products made from viscose.

The process may be used with advantage in a system wherein the first bath is a coagulating, substantially non-regenerating bath, e. g. a low acid, high zinc bath, and the second bath is a regenerating bath, and in this system, if desired, a third bath may be used for imparting stretch prior to, during or subsequent to regeneration.

The spinning bath may contain 4% to 11% sulfuric acid and 13% to 25% sodium sulfate. Zinc sulfate may be present in -amounts of about 0.5% to 20%, preferably 1% to 15%, amounts higher than 8% being preferable when zinc sulfate is used alone as the salt of the bivalent metal. In addition to zinc sulfate, there may be present sulfates of iron, nickel, magnesium, manganese or chromium in proportions up to 10%, preferably between 0.5% and Ferrous sulfate is the preferred additional ingredient. With the addition of sodium trithiocarbonate to viscose, it is possible to obtain excellent yarns in the upper range of bath acidity under which conditions, with unmodified ripened viscose, a drop in physical properties occurs. The temperature range of good spinnability is from 40 to 65 C. On the basis of available data, it is desirable to have the bath acidity and temperatures as low as is practical for a given spinning speed in order to get optimum skin thickness and yarn properties. Each of the above concentrations should be adjusted to each other and to the composition of the viscose. It is desirable to use as high total solids content as possible in the coagulating bath to give the highest degree of gel shrinkage and improved stretchability.

In using this invention for the production of high tenacity yarn, a two-bath spinning system has been employed. One procedure comprises drawing off the freshly coagulated gel yarn with a feed wheel speed equal to or less than the jet velocity and applying all of the stretch between positively driven rollers traveling at different to 50 inches in the secondary-stretching bath which may be hot water or hot dilute sulfuric acid, e. g. water containing 2% sulfuric acid. The amount of stretch applied depends on the properties desired for the-yarmany amount of stretch usedv in ,standardpractice being suitable. The invention contemplates alsothe use of a single bath system inwhich stretch is imparted to the filamentsby a series of floating tension rollers having vanes on the under side, this being a single bath system involving a relatively long bath travel -in order; to get a substantial degree of stretch. The stretch may be applied in part in the primary or coagulated bath and the remainder in air by means of a long air travel, the;;yarn remaining plastic-andresponding to stretching by virtue of the adhering bath-liquid, or the yarn may be partly in-a hotsecondary stretching bath. The

bathztravel, where a single bath is used, may be increased to 130 to 250 inches by means of a multiple floating roller setup which gradually increases the tension on the filaments and thereby orients them by stretchingthem while they are plastic. The preferred method,- however, is a two-bathsystem wherein from 60% to 100% of thestretch is imparted in a'secondary bath of boiling water or water above C. or a 2% sulfuric acid bath, the stretching bath preferably being alow acid bath; e.- g. an aqueous bath containing up to about sulfuric acid. 'A total stretchoi 80% to is preferred for producing high tenacity yarn and 20% to 30% for textile type yarns. The degree of stretch is therefore optional, dependingon the use to which the yarn istobeput." Instead of drying the" stretched yarn on the collecting bobbin as is described in the above examples, it may be partially relaxed by rewinding before'drying, on another bobbin at a lower tension. v Y

While the bobbinfprocess is illustrated in the examplesfor col ecting the yarn, the spinning maybe in accordance'with the bucket process, or conveyor belt process, oracontinuous process which involves purificationprior to collection of the yarn. In any event, the yarn is washed free of acid and salt and is dried under tension, being preferably dried as it passes to a twister, or dried on a slasher to enable a proper control of the dry elongation of the finished product. v

The skin on viscose yarn spun into sulfuric acidsodium sulfate-zinc sulfate or sulfuric "acidsodium sulfate-zinc sulfate-ferrou sulfate baths is observed and measured in the fo lowing :man ner: The dried yarn is embedded in paraffin, cross-sections are cut and "afiixed to a glass slide by a shellac cement. After removing the paraflin in xylene, the sections areswollen in water and photomicrographs are taken. The skin is the outer shell which swells to a different extent than the core so that a fairly sharp boundary exists between the skin and the core. The proportion of skin area to core area can be estimated visually or determined accurately by means of a planimeter. The skin-may be shown very graphically by a special dye technique. When cross-sections are soaked in 0.2% "Pontamine Sky Blue dye for ten to sixty minutes, the core takes on a deep blue color while the skin remains'undyed. Photomicrographs with a greatcontrast inshades in the skin and core are obtained using'appropriate red filters; Such photomicrographs are'shown in the drawings-in which are illustrated the'cross or Example 1 using a 9.5:-14.-'-1'5 (uzsoiqrazso znsoo coagulating bath, Figure 1 representing a filament spun-from unripened viscose modified in accordance, with this invention and illustrating a thick skinned filamentand Figure 2 representing a filamen t" spun from unripened, unmodified viscose and illustrating" athin skinned filament.

It is to be noted that this invention is conc had with the addition of sodium and other water soluble trithiocarbonates, as such, to the viscose? The practice of the invention distinguishes; for example, from the use of large amounts of carbon disulfide, e. g. in excess of -'50%,'= based on; the dry" weight of the cellulosein the; alkali cellulose, for the preparation of cellulose xanthate and distinguishes likewisefrom the addition of carbondisulfide as such to viscose.

T The use of large amounts of carbon disulfide inthemanner stated requires a long ripening period since normal xanthation must be carried out asusual with the ripening being longer than nor'mal i different equipment than is normally used in the viscose process and the use of airtight containers and mixers would also be required where a high carbon disulfide percentage isused. By the; addition of trithiocarbonate, on the contrary,jthe viscose composition may be readily and accurately controlled with. a close adaptation to any desired setof spinning conditions'and with the use of any carbon 'disulfide concentration dictated by the: spinning conditions and objectives. A high carbon disulflde concentration, on the other hand, necessarily changes the: xanthate sulfur concentration which seriously affects the spinning conditions. 7

r The products: of this invention in general may be used for any purposes where viscose fibers find application, for example the textile and tire'cord industries, This invention makes 'it possible to produce, yarns having a thicker skin than'isnorinally; obtained in the usuaLspinning process.

. Such-yarns have theadvantages of higher strength denier and improved fatigue resistance;- In addition, the yarns produced by'this process have improved physical properties such as wetand dry tenacitiesr l departure from the above description which conforms to the present invention is intended to be included within the scopeof the claims. r

I claim:

'1=. A process'which'comprises incorporating in a freshly formed viscose a water-soluble trithiocarbonate in excess of that formed in the preparation: of said freshly formed viscose and extruding resultant unripened viscose into a co agulating bath.

-2.'-A process which comprises modifying a freshly formed-viscose by incorporating 0.65% to about 2.15%; based on the weight of said viscose, of a Water-soluble trithiocarbonate in excess of the trith-iocarbonateformed in the preparation of said freshly formed viscos and extruding the resultant unripened viscose into a coagulating bath,

3; A process which comprises modifying a freshly formedviscose by incorporating 0.6 5% to about 2.15% of a water-soluble trithiocarbonate 'in excessof the'trithiocarbonate formed in the; preparation of said freshly; formed viscose and extruding the resultant unripened viscose 12 into a; coagulating bath comprising an aqueous solution of sulfuric acid and sodium sulfate.

4. A process which comprises modifying a freshly formed viscose by incorporating 0.65% to about 2.15% of a water-soluble trithiocarbonate in excess of the trithiocarbonate formed in the preparation of said freshly formed viscose and. extruding the resultant unripened viscose into a coagulating bath comprising an aqueous solution of sulfuric acid, sodium sulfate and a sulfate of divalent metal.

5. A process which comprises modifying a freshly formed viscose by incorporating 0.65% to about 2.15% of a water-soluble trithiocarbonate in excess of the trithiocarbonate formed in the preparation of said freshly formed viscose and extruding the resultant unripened viscose into a coagulating bath comprising an aqueous solution of sulfuric acid, sodium sulfate and. zinc sulfate.

6. A process which comprises modifying; a freshly formed viscose by incorporating 0.65% to about 2.15% of a water-soluble trithiocarbonate in excess of the trithiocarbonateformed in the, preparation of said freshly formed viscose and extruding the resultant unripened viscose into a coagulating bath comprising an aqueous solution comprising 4% to 11%; sulfuric acid, 13% to 25% sodium sulfate and 1% to 20% zinc sulfate.

'7. A process which comprises modifying a freshly formed viscose by incorporating 0.65% to 2.15% of an alkali metal trithiocarbonate in excess of the trithiocarbonate formed by the preparation of said freshly formed viscose and extruding the resultant'unripened viscose into a coagulating bath comprising an aqueous solution comprising 4% to 11% sulfuric acid, 13% to 25% sodium sulfate and 1% to 20% zinc sulfate.

8. A process which comprises modifying a freshly formed viscose by incorporating 0.65% to 2.15% of sodium trithiocarbonate in excess of the trithiocarbonate formed in the preparation of said freshly formed viscose and extruding the resultant unripened viscose into a coagulating bath comprising an aqueous solution comprising 4% to 11% sulfuric acid, 13% to 25% sodium sulfate and 1% to 20% zinc sulfate.

9. A process which comprises modifying a freshly formed viscose by adding 0.65% to 2.15% sodium trithiocarbonate in excess of that formed in the preparation of said freshly formed viscose, extruding the resultant unripened viscose as filaments into a coagulating bath comprising an aqueous solution comprising 4% to 11% sulfuric acid, 13% to 25% sodium sulfate and 1% to 20% zinc sulfate and imparting to the coagulating filaments a substantial degree of stretch.

10. A process which comprises modifying a freshly formed viscose by incorporating 0.65% to 2.15% sodium trithiocarbonate in excess. of the trithiocarbonate formed in the preparation of said freshly formed viscose; extruding the resultant unripened viscose as filaments into a coagulating bath comp-rising an aqueous solution comprising 4% to 11% sulfuric acid, 13% to 25% sodium sulfate and 1% to 20% zinc sulfate and imparting to the coagulating filaments a stretch of at least 20%. v

a 11. The process of claim 10 in which the stretch is at least 20% and is applied at least in part in a secondary bath.

NORMAN LOUIS COX.

. (References on followingpage) 13 14 REFERENCES CITED FOREIGN PATENTS The following references are of record in the Number Country Date file of this patent: 370,359 Great Britain Sept. 29, 1930 778,947 France Mar, 26, 1935 UNITED STATES PATENTS OTHER REFERENCES Number Name Date 1,683,199 Lilienfeld Sept. 4, 1938 High Polymers, Vol. V, Cellulose and Cellulose 2,324,437 Soukup July 13, 1943 Derivatives, Ott, 1943, pages 821-322.

2,347,884 Cox May 2, 1944 Berl et 9.1.: Cellulose Chemie, VII, No. 10,

2,348,415 Polak May 9, 1944 10 October 3, 1926, page 142. 

1. A PROCESS WHICH COMPRISES INCORPORATING IN A FRESHLY FORMED VISCOSE A WATER-SOLUBLE TRITHIOCARBONATE IN EXCESS OF THAT FORMED IN THE PREPARATION OF SAID FRESHLY FORMED VISCOSE AND EXTRUDING RESULTANT UNRIPENED VISCOSE INTO A COAGULATING BATH. 